Metal Zone is my least favourite distortion pedal - I find it a bit of a tone killer. Like everyone else I used to think putting distortion to 10 on the dial got the heaviest sound, this of course is very wrong. The heaviest sounds come from lower levels of distortion - from between 6 - 8.
As far as pedals/stomp boxes go, the best I've used is the Line6 DM4
http://line6.com/stompboxmodelers/dm4.html

The Metal Zone tone is in there along with just about every other distortion/overdrive pedal you can think of including the Ibanez Tube Screamer. The sound is leagues ahead of PODxt distortions to my ear - much more ballsy and real. Usually I'm not a big fan of Line6 but the DM4 is a great piece of gear. Worth checking out as a one stop shop for metal tones.